Sample and hold

In electronics, a sample and hold (S/H, also "follow-and-hold"[1]) circuit is an analog device that samples (captures, takes) the voltage of a continuously varying analog signal and holds (locks, freezes) its value at a constant level for a specified minimum period of time. Sample and hold circuits and related peak detectors are the elementary analog memory devices. They are typically used in analog-to-digital converters to eliminate variations in input signal that can corrupt the conversion process.[2] They are also used in electronic music, for instance to impart a random quality to successively-played notes (for example, in the bass line to Jan Hammer's "Don't You Know".[3])

A typical sample and hold circuit stores electric charge in a capacitor and contains at least one switching device such as a FET (field effect transistor) switch and normally one operational amplifier.[1] To sample the input signal the switch connects the capacitor to the output of a buffer amplifier. The buffer amplifier charges or discharges the capacitor so that the voltage across the capacitor is practically equal, or proportional to, input voltage. In hold mode the switch disconnects the capacitor from the buffer. The capacitor is invariably discharged by its own leakage currents and useful load currents, which makes the circuit inherently volatile, but the loss of voltage (voltage drop) within a specified hold time remains within an acceptable error margin.

A simplified sample and hold circuit diagram. AI is an analog input, AO — an analog output, C — a control signal.

Sample times.

Sample and hold.

Purpose

Sample and hold circuits are used in linear systems. In some kinds of analog-to-digital converters, the input is compared to a voltage generated internally from a digital-to-analog converter (DAC). The circuit tries a series of values and stops converting once the voltages are equal, within some defined error margin. If the input value was permitted to change during this comparison process, the resulting conversion would be inaccurate and possibly unrelated to the true input value. Such successive approximation converters will often incorporate internal sample and hold circuitry. In addition, sample and hold circuits are often used when multiple samples need to be measured at the same time. Each value is sampled and held, using a common sample clock.

For practically all commercial liquid crystalactive matrix displays based on TN, IPS or VA electro-optic LC cells (excluding bi-stable phenomena), each pixel represents a small capacitor, which has to be periodically charged to a level corresponding to the greyscale value (contrast) desired for a picture element. In order to maintain the level during a scanning cycle (frame period), an additional electric capacitor is attached in parallel to each LC pixel to better hold the voltage. A thin-film FET switch is addressed to select a particular LC pixel and charge the picture information for it. In contrast to an S/H in general electronics, there is no output operational amplifier and no electrical signal AO. Instead, the charge on the hold capacitors controls the deformation of the LC molecules and thereby the optical effect as its output. The invention of this concept and its implementation in thin-film technology have been honored with the IEEE Jun-ichi Nishizawa Medal.[4]

During a scanning cycle, the picture doesn’t follow the input signal. This does not allow the eye to refresh and can lead to blurring during motion sequences, also the transition is visible between frames because the backlight is constantly illuminated, adding to display motion blur.[5][6]

Implementation

To keep the input voltage as stable as possible, it is essential that the capacitor have very low leakage, and that it not be loaded to any significant degree which calls for a very high input impedance.

The ARP Odyssey is an analog synthesizer introduced in 1972. Responding to pressure from Moog Music to create a portable, affordable (the Minimoog was US$1,495 upon release) "performance" synthesizer, ARP Instruments, Inc. scaled down its ARP 2600 synthesizer and created the Odyssey, which became their best-selling synthesizer model.

There were several versions of the Odyssey over the years, and it was reissued by Korg in early 2015, in cooperation with the original designer and ARP co-founder, David Friend.The ARP Odyssey was used as the lead for Peter Howell's incarnation of the Doctor Who theme.

In electronics, an analog-to-digital converter (ADC, A/D, or A-to-D) is a system that converts an analog signal, such as a sound picked up by a microphone or light entering a digital camera, into a digital signal. An ADC may also provide an isolated measurement such as an electronic device that converts an input analog voltage or current to a digital number representing the magnitude of the voltage or current. Typically the digital output is a two's complement binary number that is proportional to the input, but there are other possibilities.

There are several ADC architectures. Due to the complexity and the need for precisely matched components, all but the most specialized ADCs are implemented as integrated circuits (ICs).

A digital-to-analog converter (DAC) performs the reverse function; it converts a digital signal into an analog signal.

Dewtron (Design Engineering (Wokingham) Ltd. or D. E. W. Ltd.) were a small British manufacturer of modular synthesizers which were sold to customers in kit form or as built units. It was founded by Brian Baily on 5 February 1964 in Wokingham, Berkshire. By 1970 the company's products included oscillators, voltage controlled amplifiers, sample and hold and envelope shapers.Mike Rutherford used a Dewtron "Mister Bassman" bass pedal synthesizer on Genesis albums from Nursery Cryme (1971) onwards, before replacing it with a Moog Taurus I for the album A Trick of the Tail (1976). Yes' frontman Jon Anderson used a similar unit in live performances. Chris Carter, later to form Throbbing Gristle, experimented with Dewtron kit-based synthesizers early in his music career.The company later moved to the Ferndown area in Dorset (near Wimborne Minster) and shipped some synthesizer modules and related products from there before closing.

Display motion blur, also called HDTV blur and LCD motion blur, refers to several visual artifacts (anomalies or unintended effects affecting still or moving images) that are frequently found on modern consumer high-definition television sets and flat panel displays for computers.

A drop-out compensator is an error concealment device that was commonly used in the analog video era to hide brief RF signal "drop-outs" on videotape playback caused by imperfections in or damage to the tape's magnetic coating. Most compensators worked by repeating earlier video scan-lines over short periods of signal loss; one early such system, "Mincom" was developed in the 1960s by the Minnesota Mining and Manufacturing Company, the company now known as 3M. Because of the high cost of the 3M device at the time, BBC R&D engineers developed a simpler, less expensive unit based on a sample-and-hold technique for in-house use.Dedicated drop-out compensators were eventually superseded by the incorporation of drop-out compensation functionality into timebase correctors based on analog-to-digital conversion and digital line stores.

The advent of compressed digital video systems finally eliminated the need for line-based drop-out compensators. Most low-level media errors, such as those caused by tape damage or imperfections, are now dealt with by forward error correction techniques, and those which overwhelm the FEC layer are typically too severe to remedy using simple line-based error concealment techniques, because damage to the compressed bitstream will often damage large parts of the video image. However, since occasional signal drop-outs can still occur, either through severe tape damage or because of packet loss in packetized video transmission, modern error concealment techniques that are aware of the structure of the compressed video format have been developed to deal with these.

Effective number of bits (ENOB) is a measure of the dynamic range of an analog-to-digital converter (ADC) and its associated circuitry. The resolution of an ADC is specified by the number of bits used to represent the analog value, in principle giving 2N signal levels for an N-bit signal. However, all real ADC circuits introduce noise and distortion. ENOB specifies the resolution of an ideal ADC circuit that would have the same resolution as the circuit under consideration.

ENOB is also used as a quality measure for other blocks such as sample-and-hold amplifiers. This way, analog blocks can be easily included in signal-chain calculations, as the total ENOB of a chain of blocks is usually below the ENOB of the worst block.

The frequency band of a signal converter where ENOB is still guaranteed is called the effective resolution bandwidth and is limited by dynamic quantization problems.

A field-programmable analog array (FPAA) is an integrated circuit device containing computational analog blocks (CAB) and interconnects between these blocks offering field-programmability. Unlike their digital cousin, the FPGA, the devices tend to be more application driven than general purpose as they may be current mode or voltage mode devices. For voltage mode devices, each block usually contains an operational amplifier in combination with programmable configuration of passive components. The blocks can, for example, act as summers or integrators.

FPAAs usually operate in one of two modes: continuous time and discrete time.

Discrete-time devices possess a system sample clock. In a switched capacitor design, all blocks sample their input signals with a sample and hold circuit composed of a semiconductor switch and a capacitor. This feeds a programmable op amp section which can be routed to a number of other blocks. This design requires more complex semiconductor construction. An alternative, switched-current design, offers simpler construction and does not require the input capacitor, but can be less accurate, and has lower fan-out - it can drive only one following block. Both discrete-time device types must compensate for switching noise, aliasing at the system sample rate, and sample-rate limited bandwidth, during the design phase.

Continuous-time devices work more like an array of transistors or op amps which can operate at their full bandwidth. The components are connected in a particular arrangement through a configurable array of switches. During circuit design, the switch matrix's parasitic inductance, capacitance and noise contributions must be taken into account.Currently there are very few manufactures of FPAAs. On-chip resources are still very limited when compared to that of an FPGA. This resource deficit is often cited by researchers as a limiting factor in their research.

The High Resolution Fly's Eye or HiRes detector was an ultra-high-energy cosmic ray observatory that operated in the western Utah desert from May 1997 until April 2006. HiRes utilized the atmospheric fluorescence technique that was pioneered by the Utah group first in tests at the Volcano Ranch experiment and then with the original Fly's Eye experiment. Dr. Pierre Sokolsky and Dr. George Cassidy, both of the University of Utah, received the 2007 Panofsky Prize for their work on this.

The High Resolution Fly's Eye used larger mirrors and smaller pixels as compared with the original Fly's Eye, hence the name. A prototype of the HiRes experiment operated between 1993–1996 at the original Fly's Eye-I site (Five Mile Hill). It was configured in a tower viewing a narrow wedge of sky from 3–73 degrees in elevation. First the Utah ground array and later the CASA and MIA (ground array and muon array) experiments were placed on the surface in the view of the HiRes prototype. This then became the first "hybrid experiment" collecting information both on the development of the air shower induced by the incident cosmic ray, but also measuring the shower's footprint at the Earth's surface and 3 m below surface (with the buried muon array). The HiRes prototype was disassembled early in 1997 to become part of the final HiRes configuration.

In its final configuration, HiRes was composed of two sites separated by 12.6 km. The sites were located on hilltops in Dugway Proving Grounds, a U.S. Army test facility in the west Utah desert. HiRes-I (located on Five Mile Hill or Little Granite Mountain(40.1953°N 112.8363°W﻿ / 40.1953; -112.8363)) had one ring of 22 telescopes viewing from 3–17 degrees in elevation. HiRes-I was instrumented with sample and hold electronics which took a "snapshot" of the extensive air shower generated when the incident cosmic ray interacted with the atmosphere. Meanwhile, HiRes-II (located on Camel's Back Ridge(40.13194°N 112.95896°W﻿ / 40.13194; -112.95896)) had two rings of telescopes to provide viewing higher into the atmosphere. It observed from 3 to 31 degrees in elevation. HiRes-II was instrumented with an FADC (Flash Analog to Digital Converter) so that it essentially made movies of the cosmic ray events. Both observatory sites provided full azimuthal coverage (360 degrees in azimuth). They were operated independently on moonless clear nights. The duty cycle of HiRes was close to 10%.

The HiRes experiment made the first observation of the GZK cutoff which is an indication of the highest energy cosmic rays interacting with the Cosmic Microwave Background and the universe becoming opaque to their propagation.

In 2010 final results of the HiRes experiment confirmed the GZK cutoff.A follow-on experiment to the High Resolution Fly's Eye and Akeno Giant Air Shower Array (AGASA) experiments is the Telescope Array Project which began data collection in central Utah in 2007. Similar approach, but with the water-Cherenkov detectors, has been employed for the Pierre Auger Observatory which began collecting data in 2004.

The Moog model 2090 Micromoog is a monophonic analog synthesizer produced by Moog Music from 1975–79.

During 1973 & 74, Moog attempted to produce a synth system, possibly as a result of seeing Yamaha's massive GX-1. The bass and polyphonic components of the "Constellation" became the Taurus and PolyMoog, and while the Lyra monophonic lead synth never went into production, the smaller MicroMoog emerged, using some of the ideas and technology.

The monophonic Micromoog was designed by Moog Engineer Jim Scott in consultation with Tom Rhea, with electronic refinement input from David Luce, Robert Moog, as a scaled-down, cheaper alternative ($650-$800 market price) to the Minimoog. It was designed to tap into a market of musicians who wanted an introduction to synthesis, but who could not afford the $1,500 Minimoog. However, while the basic architecture was a simple VCO/VCF/VCA, inexpensive enhancements made it a more creative synth. Its single voltage-controlled oscillator has variable waveshape which can also be modulated and a sub-octave can be added one or two octaves below. Its -24 dB per octave low-pass filter has its own envelope generator, and can be frequency modulated by the VCO. The voltage-controlled amplifier has its own envelope generator. A noise generator, sample and hold, low-frequency oscillator, and modulation routing complete the voicing. Moog chose to use two A(S)R envelope generators (with switchable sustain) instead of the single ADSR more commonly found on budget synths. Other switches like VCA bypass, VCF tone mode and release on/off allow quick changes to be made live.

It has a 32-note keyboardwith a built-in ribbon controller instead of the more common pitch bend wheel, although a retrofit pitch bend wheel was available.

The Micromoog also features the Moog Open System control inputs, a pre-MIDI control system which enables the unit to control or be controlled by other Moog synthesizers, even suggesting using it with Moog modules and sequencer. Unusually, the CV inputs were designed to operate at 0.95v per octave - the idea being that the 1v/octave outputs of synths could get loaded down, but could still be used into the Micromoog. In practice, this is a pain and in many cases, people have attempted to tweak the tracking, but the best that can be achieved without modification is around 0.98v per octave. Triggering is Moog standard S-triggering on Cinch Jones connectors. Modulation in/out is on a stereo 3/16" jack - a difficult connector to find. An "access pwr" socket is provided for connection of Moog accessories such as the drum controller, sample and hold and ribbon controller.

Early Micromoogs had slightly different panel labelling - from serial number 1500 "Articulator" become "Loudness Contour". Later Micromoogs also gained an extra potentiometer on the back to adjust the keyboard output tracking. There were also internal changes to the keyboard.

The Micromoog has an audio input allowing external audio to be run through the filter and VCA.

The Micromoog served as the basis for the Multimoog, a similarly styled, but more generously equipped synthesizer featuring two VCOs, a larger 44 note keyboard, greater modulation options and an early implementation of keyboard aftertouch functions.

The Moog Rogue is a monophonic analog synthesizer produced by the original Moog Music in the early 1980s, but, was not designed by Bob Moog. Very basic in its design and use, the Rogue featured a 32-note keyboard and two VCOs. VCO number 2 is tunable between a half-step below to an octave above VCO number 1. This allows the Rogue to play atonal sounds like the Moog Prodigy. The Rogue did not have features to allow the user full flexibility to program the patch settings, however the VCF and the VCA were simple in operation. The design of the hard-wired patch system was well thought out (considering its size and cost) and a wide variety of sounds and modulation effects are possible. The Rogue also includes a Sample-and-Hold feature that the Prodigy does not. The synthesizer is most commonly used for its powerful bass. The Rogue is similar in some respects to the famous ARP Odyssey, though smaller and slightly less versatile.

Moog Music was criticized for repackaging the Rogue as the Taurus II, changing the design to a pedal-operated synthesizer with little difference in sound quality.

The Rogue is very similar in design and sound to the less-expensive Moog Concertmate MG-1, also made by Moog Music, but re-branded for Realistic around the same time for home use. This was perhaps the first example of a keyboard designed for the home musician.

The Moog Source is a monophonic Z80 microprocessor-controlled analog synthesizer manufactured by Moog Music from 1981 to 1985. The Source was Moog's first synthesizer to offer patch memory storage. The design was also the first (and only) Moog synthesizer to feature a flat-panel membrane keyboard to replace the standard buttons, knobs and sliders, along with multihued panel graphics that were very different from anything Moog offered at the time. Sound wise it is considered to sound more like the original Moog Minimoog than any other synthesizer made by Moog and was introduced as its replacement.

In addition to the memory capable of holding 16 presets, the Source features a 37-note keyboard, and two VCOs that can be selected among three waveforms and three octaves. Programmed presets can be saved to an audio cassette interface to free up the onboard memory for additional new patches. The 24dB/octave VCF has parameters for keyboard tracking, cutoff frequency, resonance, and envelope amount. There are two ADSR envelope generators that can be set in single or multi trigger modes, one for the VCF and one for the VCA. For modulation, the Source features LFO and sample and hold. The unit also features a rudimentary sequencer. The Source was made in at least 2 versions the latter offering more voltage control options. A modification offered by Encore Electronics offers the addition of MIDI, increased memory and more sequence storage.

Neil Young in Berlin is a live video by Neil Young, directed by Michael Lindsay-Hogg, and recorded in October, 1982 during the European Tour of his album Trans. It was issued on VHS Video (1983) & later on DVD.

The SH-3A is a monophonic analog synthesizer that was manufactured by Roland from 1974 to 1981. It is unique in that it is capable of both subtractive synthesis and additive synthesis. Two LFOs and a unique sample-and-hold section provided capabilities not found in competing self-contained synthesizers of the time. The SH-3A was Roland's first non-preset based synth. It was unique for its time in that it offered mixable waveforms at different footages. The predecessor, the Roland SH-1000 could also do this but didn't offer as much control as on the SH-3A. The rhythmic pulsing in the Blondie song "Heart of Glass" is an example of its sound.

Contrary to common belief, the initial version "SH-3" did not infringe on the transistor ladder-filter patent of Robert Moog. It used a diode filter like the EMS VCS 3. The SH-3A does use a transistor ladder-filter and as a result can generate Moog-like sounds.

The Roland System 100 was an analog semi-modular synthesizer (having an internal fixed signal path that could be overridden by plugging patch cables into the front of the synth) manufactured by Japan's Roland Corporation, released in 1975 and manufactured until 1979. It consisted of the following products:

Expander 102 The same synthesizer again, without the keyboard, to be stood up behind the 101 and patched into it in order to double its features. In addition, a ring modulator and sample and hold are included.

Sequencer 104 A two-channel, 12-step sequencer to automate playing looped bars of notes.

Monitor speaker 109 A pair of 16cm speakers.

PCS-10 20cm, 40cm, 60cm, 80cm and 1m patch cables.

While the System 100 was not fully modular, unlike the later Roland System-100M and the Roland System 700, a complete system nevertheless formed an expandable two-oscillator monosynth with sequencing, monitoring and effects capabilities. Each unit was independently powered, so complex patches wouldn't cause either oscillator to drop in pitch. Uniquely for the time, the System 100 didn't "lock in" the oscillators to fixed footages or pitches, allowing greater flexibility for sound design. It uses the 1V/oct standard, so can be used with a MIDI-to-CV converter.

The System 100 is still sought-after due to its filter, sequencer and patching capabilities, though the oscillators can be unstable at the lower frequencies, and the keyboard is prone to mis-triggering and double-triggering if not used regularly. Generally, however, it is a robust and reliable system. The SH-5 and SH-7 are similar in styling, but both have fixed signal paths, as opposed to the semi-modular System 100.

The Schottky diode (named after the German physicist Walter H. Schottky), also known as Schottky barrier diode or hot-carrier diode, is a semiconductor diode formed by the junction of a semiconductor with a metal. It has a low forward voltage drop and a very fast switching action. The cat's-whisker detectors used in the early days of wireless and metal rectifiers used in early power applications can be considered primitive Schottky diodes.

When sufficient forward voltage is applied, a current flows in the forward direction. A silicon diode has a typical forward voltage of 600–700 mV, while the Schottky's forward voltage is 150–450 mV. This lower forward voltage requirement allows higher switching speeds and better system efficiency.

Unplugged is a live album by Canadian singer-songwriter Neil Young, released on June 15, 1993 on Reprise. Recorded on February 7, 1993, the album is an installment of the MTV series, Unplugged. The performance was also released on VHS.

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